1. Field of the Invention
This invention relates generally to ventilation systems and methods, and more particularly to self-contained heating, ventilation, and air conditioning (HVAC) control systems. Even more particularly, the invention relates to HVAC flow control systems which are suitable for prefabrication and installation as a unit.
2. Description of the Background Art
In many circumstances it is desirable to maintain a positive pressure in a room or work area, relative to adjoining rooms, hallways, etc. For example, a positive pressure inside a hospital operating room prevents airborne contaminants from entering the room when doors are opened. The positive pressure inside the room causes air to flow out of instead of in through open doors. Similarly, a positive pressure inside a room ensures that unwanted fumes flow efficiently out through exhaust vents (e.g., vent hoods, isolation cabinets, etc.), rather than backing up into the room.
Flow controllers are known that control the flow rate of air through a vent. Such flow controllers are typically installed as part of an HVAC system. Construction workers on site mount the controllers in air ducts of the HVAC system. The installation is labor intensive, and therefore very expensive.
In some circumstances, it is also desirable to be able to isolate a room or an area from the ventilation system of the rest of a structure. For example, isolation of a particular room can prevent a toxic release (e.g., a gas leak) from contaminating other areas. In the case of certain toxic gasses, effective isolation can mean the difference between life and death for workers in adjoining areas. As another example, isolation of a section of an HVAC system facilitates decontamination of the isolated section, without contaminating or shutting down the entire HVAC system. Known flow controllers are unsuitable for isolation applications, because their leakage ratings are typically greater than or equal to eight percent.
Further, in certain critical applications it is desirable to pretest and/or precertify components of a system prior to shipping and installation. Components of an HVAC system that are separately installed on site cannot be pretested and/or precertified as a unit. If the components do not meet predetermined criteria after installation, the components must be torn out and substitute components installed. Such rebuilds are also very labor intensive and expensive.
Another problem with precertifying components before they are installed is that the function of a component can depend on other components and installation specifics. For example, flow sensors can give different readings depending on the amount of turbulence in the flowing air. Thus, readings provided by sensors can depend on whether the sensor is disposed in a straight section of duct or adjacent to a bent section of duct. As another example, air flow rate through a flow controller can depend on other components (e.g., heating coils) in the path of the air flow.
What is needed, therefore, is a flow control system for controlling the flow of air into a confined space. What is also needed is a ventilation flow control system that can effectively isolate sections of an HVAC system. What is also needed is a flow control system that can be tested and/or certified prior to installation. What is also needed is a method of installing a flow control system that is less labor intensive than current methods, and lends itself to preinstallation testing and/or certification of the components.